Add legacy rollout migration to paginated history (#37175)

## What changed

- Add `LocalThreadStore::migrate_rollouts` with dry-run and apply modes,
  optional thread selection, throughput limiting, and per-rollout outcomes.
- Canonicalize legacy JSONL records into paginated history while preserving
  model-visible conversation context, including compressed rollouts and copied
  fork history.
- Publish replacements atomically and journal migrations so interrupted SQLite
  projections can be recovered. Coordinate migration with rollout compression
  and skip rollouts with active writers.
- Make paginated history a one-way SQLite promotion so stale metadata cannot
  downgrade a migrated thread.

## Testing

- Cover legacy record normalization, dry runs, idempotency, malformed input,
  compressed rollouts, active writers, interrupted migration recovery, and a
  cold app-server resume after migration.

GitOrigin-RevId: b9991b659f28ebb52da39ce62e8b4e0bae2ba2bb

codex-rs/thread-store/src/local/mod.rs

@@ -8,6 +8,7 @@ mod model_context;
 mod move_thread_to_section;
 mod paginated_fork;
 mod read_thread;
+mod rollout_migration;
 // This lands before the reader PRs that consume the shared lineage resolver.
 #[allow(dead_code)]
 mod rollout_lineage;
@@ -78,6 +79,12 @@ use crate::UpdateThreadMetadataParams;
 use crate::local::writer_lock::WriterLockCoordinator;
 use crate::local::writer_lock::WriterLockGuard;
 
+pub use rollout_migration::RolloutMigrationMode;
+pub use rollout_migration::RolloutMigrationOptions;
+pub use rollout_migration::RolloutMigrationOutcome;
+pub use rollout_migration::RolloutMigrationReport;
+pub use rollout_migration::RolloutMigrationStatus;
+
 /// Local filesystem/SQLite-backed implementation of [`ThreadStore`].
 ///
 /// Local storage has two compatibility surfaces. Rollout JSONL files are the